1. Field of Invention
The invention relates to a device for the transportation of a film tube in which the film tube is guided by at least one first film guide element, at least one second film guide element, and at least one third film guide element such that the film tube can discharge heat to the surrounding environment in the area of the film guide elements.
2. Description of the Prior Art
A device of this kind is already known. It is used in general in equipment for the production of film tubes or film sheets. Plastic materials in granulated form are fed into such equipment, which are then plasticized into a viscous mass under the action of high pressure in the extruder. This mass, which has a high temperature due to the pressure, is formed into a ring-like form in a die head and comes out of the die head through a tubular die. The mass forms a film tube already immediately after leaving the tubular die. After passing through a so-called calibration basket, the film tube is guided along by the other film guide elements, which flatten the tube. Frequently, this flattening unit feeds to a pre-squeezer of the film tube, so that it forms an almost double-layered film sheet. The pre-squeezer consists mostly of a pair of rollers, through the clearance between which rollers, the film passes through. The pre-squeezer is followed by a squeezer, in which from the film tube finally a double-layered film sheet is formed. The distance from the pre-squeezer to the squeezer is so dimensioned that the film sheet can release the heat stemming from the extrusion process in course of the transport between the roller pairs. The film tube is thus additionally cooled in this manner, so that it can be processed further. This includes, for example, the separation of the film tubes, so that two film sheets are formed, and/or the winding of the film tube or the film sheet. This type of cooling of the film tube can, however, take place in general at least between two arbitrary film guide elements.
The only requirement is that there is a possibility that the film tube can discharge the heat to its environment.
In known devices of this type, there is however frequently the problem that—depending on the film type and the thickness of the film—the film tube cannot cool down between the two guide elements adequately for the subsequent processing. In particular, if it is not adequately cooled, it can result in sticking together of the double-layered film sheet, so that a subsequent drawing apart, for instance during the production and the filling of the bags made from the film tube, is not or no longer possible without damage. On the other hand, too much cooling of the film can lead to undesired stiffness of the same, so that it tends to develop folds or ruptures in course of the subsequent processing steps.